Motor control apparatus and motor control method

ABSTRACT

An increase in angular acceleration α of a rotating shaft of a motor, which outputs a torque to a drive shaft linked to drive wheels, may cause a skid on the drive wheels. In response to detection of a skid, the control procedure of the invention sets a maximum torque Tmax according to a preset map representing a relation between the angular acceleration α and the maximum torque Tmax, and restricts an output torque level to the drive shaft. The map is set to decrease the maximum torque Tmax with an in crease in angular acceleration α. The restricted output torque level is restored at a zero cross timing of the angular acceleration α after a negative peak in the course of convergence of the skid. This arrangement makes the direction of the torque restored from the torque restriction identical with the direction of the angular acceleration, thus effectively reducing torsions of the drive shaft and thereby preventing potential torsional vibrations of the drive shaft.

This is a 371 national phase application of PCT/JP2003/008594 filled 7Jul. 2003, claiming priority to Japanese Patent Application No.2002-251365 filed 29 Aug. 2002, the contents of which are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a motor control apparatus and a motorcontrol method. More specifically the invention pertains to a motorcontrol apparatus that controls a motor, which is mounted on a vehicleand outputs power to a drive shaft linked to drive wheels, as well as toa corresponding motor control method.

BACKGROUND ART

One proposed motor control apparatus of controlling a motor mounted on avehicle restricts an output torque level from the motor to a driveshaft, in response to detection of wheelspin of drive wheels caused bythe torque output from the motor (see, for example, Japanese PatentLaid-Open Gazette No. 2001-295676). This known motor control apparatusdetects the occurrence of a skid in response to an increase in angularacceleration of the drive wheels (that is, a time variation of angularvelocity) over a predetermined threshold value and lowers the outputtorque level from the motor. The restricted output torque level from themotor is restored, in response to detection of convergence of the skid.

In the prior art motor control apparatus, however, restoration of therestricted output torque level may cause vibrations of a rotating shaftof the motor (vibrations of a driving system). Reduction of a skidarising on the drive wheels is generally accompanied with a vibration ofthe angular acceleration. The vibration of the angular acceleration maybe amplified by restoration of the restricted output torque level at aninadequate timing.

DISCLOSURE OF THE INVENTION

The motor control apparatus and the corresponding motor control methodof the invention aim to prevent potential vibrations of a driving systemin the course of skid control.

At least part of the above and the other related objects is attained bythe motor control apparatus and the corresponding motor control methodof the invention having the arrangements discussed below.

A first motor control apparatus of the invention controls a motor, whichis mounted on a vehicle and outputs power to a drive shaft linked todrive wheels, and includes: an angular acceleration measurement modulethat measures an angular acceleration of either the drive shaft or arotating shaft of the motor; a skid detection module that detectsoccurrence of a skid due to wheelspin of the drive wheels, in responseto an increase in measured angular acceleration over a preset value; afirst torque restriction control module that, in response to detectionof the occurrence of a skid by the skid detection module, sets a certaintorque restriction rate to restrict an output torque level for reductionof the skid and controls the motor with the restricted output torquelevel; and a torque restoration control module that restores the outputtorque level restricted by the first torque restriction control moduleand controls the motor with the restored output torque level at apredetermined timing when the angular acceleration measured by theangular acceleration measurement module has an increase in the course ofconvergence of the skid.

In response to detection of the occurrence of a skid due to wheelspin ofthe drive wheels with an increase in angular acceleration of the driveshaft over the preset value, the first motor control apparatus of theinvention restricts the output torque level to the drive shaft forreduction of the detected skid. The restricted output torque level isrestored at the predetermined timing when the angular acceleration hasan increase in the course of convergence of the skid by the restrictionof the output torque level. Namely the restricted output torque level isrestored at the timing when the direction of the torque applied on thedrive shaft in the course of restoration from the torque restriction iscompletely identical with the direction of the angular accelerationapplied on the drive shaft. This arrangement thus effectively reducestorsions of the drive shaft in the course of restoration of therestricted output torque level and thereby prevents potential torsionalvibrations of the drive shaft.

In the first motor control apparatus of the invention, the predeterminedtiming may represent a change timing of the measured angularacceleration from negative to positive. This arrangement moreeffectively prevents the potential torsional vibrations of the driveshaft.

In the first motor control apparatus of the invention, the torquerestoration control module may control the motor with a lower torquerestriction rate than the certain torque restriction rate set by thefirst torque restriction control module for a preset time period, so asto restore the restricted output torque level. This arrangement moreeffectively prevents the potential torsional vibrations of the driveshaft.

The first motor control apparatus of the invention may further include:a second torque restriction control module that controls the motor withsetting of a specified torque restriction, when an absolute value of afirst negative peak of the measured angular acceleration detected afterthe increase over the preset value is greater than a predeterminedthreshold value. The negative peak of the angular acceleration isexpected to reflect a change of the road surface condition. Thespecified torque restriction corresponding to the change of the roadsurface condition for the predetermined time period desirably preventsthe potential torsional vibrations of the drive shaft caused by thechanging road surface condition. In the first motor control apparatusstructured in this way, the second torque restriction control module maycontrol the motor with a torque restriction rate set corresponding tothe absolute value of the first negative peak as the specified torquerestriction. Further, in the first motor control apparatus of theinvention, the second torque restriction control module may control themotor with the setting of the specified torque restriction for apredetermined time period.

Moreover, in the first motor control apparatus of the invention, thefirst torque restriction control module may control the motor to have atorque variation in a preset allowable range. This arrangement desirablyreduces a potential torque shock due to restriction of the output torquelevel to the drive shaft in response to detection of the occurrence of askid.

A second motor control apparatus of the invention controls a motor,which is mounted on a vehicle and outputs power to a drive shaft linkedto drive wheels, and includes: a skid detection module that detectsoccurrence of a skid due to wheelspin of the drive wheels; a torquerestriction rate setting module that, in response to detection of theoccurrence of a skid by the skid detection module, sets a torquerestriction rate of torque output to the drive shaft corresponding to adegree of the detected skid; a torque restriction rate correction modulethat, when control of the motor with the set torque restriction ratemakes a torque variation out of a preset allowable range, corrects thetorque restriction rate to limit the torque variation in the presetallowable range; and a torque restriction control module that controlsthe motor, based on a power demand to the drive shaft and the set orcorrected torque restriction rate.

In response to detection of the occurrence of a skid due to wheelspin ofthe drive wheels, the second motor control apparatus of the inventionsets the torque restriction rate of torque output to the drive shaftcorresponding to the degree of the detected skid. When control of themotor with the set torque restriction rate makes a torque variation outof the preset allowable range, the torque restriction rate is correctedto limit the torque variation in the preset allowable range. The motoris controlled, based on the power demand to the drive shaft and the setor corrected torque restriction rate. The torque restriction rate setcorresponding to the degree of the detected skid is regulated to limitthe torque variation of the motor in the preset allowable range. Thisarrangement thus effectively reduces a potential torque shock caused byrestriction of the torque output to the drive shaft (a decrease intorque level) in response to the occurrence of a skid.

The second motor control apparatus of the invention may further include:an angular acceleration measurement module that measures an angularacceleration of either the drive shaft or a rotating shaft of the motor.In this embodiment, the skid detection module may detect the occurrenceof a skid when the measured angular acceleration exceeds a predeterminedthreshold value, and in response to detection of the occurrence of askid by the skid detection module, the torque restriction rate settingmodule may set the torque restriction rate of torque output to the driveshaft corresponding to the angular acceleration measured by the angularacceleration measurement module. Further, in the second motor controlapparatus of the invention, the torque restriction rate setting modulemay increase the torque restriction rate with an increase in angularacceleration.

A first motor control method of the invention controls a motor, which ismounted on a vehicle and outputs power to a drive shaft linked to drivewheels, and includes the steps of: (a) measuring an angular accelerationof either the drive shaft or a rotating shaft of the motor; (b)detecting occurrence of a skid due to wheelspin of the drive wheels, inresponse to an increase in measured angular acceleration over a presetvalue; (c) in response to detection of the occurrence of a skid, settinga certain torque restriction rate to restrict an output torque level forreduction of the skid and controlling the motor with the restrictedoutput torque level; and (d) restoring the output torque levelrestricted in the step (c) and controlling the motor with the restoredoutput torque level at a predetermined timing when the angularacceleration measured in the step (a) has an increase in the course ofconvergence of the skid by the restriction of the output torque level.

In the first motor control method of the invention, the predeterminedtiming may represent a change timing of the measured angularacceleration from negative to positive.

In the first motor control method of the invention, the step (d) maycontrol the motor with a lower torque restriction rate than the certaintorque restriction rate set by the said step (c) for a preset timeperiod, so as to restore the restricted output torque level.

The first motor control method of the invention may further include thestep of: (e) controlling the motor with setting of a specified torquerestriction, when an absolute value of a first negative peak of themeasured angular acceleration detected after the increase over thepreset value is greater than a predetermined threshold value. In thefirst motor control method of the invention, the step (e) may controlthe motor with a torque restriction rate set corresponding to theabsolute value of the first negative peak as the specified torquerestriction. Further, in the first motor control method of theinvention, the step (e) may control the motor with the setting of thespecified torque restriction for a predetermined time period.

A second motor control method of the invention controls a motor, whichis mounted on a vehicle and outputs power to a drive shaft linked todrive wheels, and includes the steps of: (a) detecting occurrence of askid due to wheelspin of the drive wheels; (b) in response to detectionof the occurrence of a skid by the step (a), setting a torquerestriction rate of torque output to the drive shaft corresponding to adegree of the detected skid; (c) when control of the motor with the settorque restriction rate makes a torque variation out of a presetallowable range, correcting the torque restriction rate to limit thetorque variation in the preset allowable range; and (d) controlling themotor, based on a power demand to the drive shaft and the set orcorrected torque restriction rate.

The second motor control method of the invention may further include thestep of: (e) measuring an angular acceleration of either the drive shaftor a rotating shaft of the motor, prior to the step (a). In thisembodiment, the step (a) may detect the occurrence of a skid when theangular acceleration measured by the step (e) exceeds a predeterminedthreshold value, and in response to detection of the occurrence of askid by the step (a), the step (b) may set the torque restriction rateof torque output to the drive shaft corresponding to the angularacceleration measured by the step (e).

The technique of the invention is not restricted to the motor controlapparatus or the corresponding motor control method discussed above, butmay also be actualized by a vehicle equipped with a motor and the motorcontrol apparatus of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates the configuration of an electricvehicle 10 equipped with a motor control apparatus 20 in one embodimentof the invention;

FIG. 2 is a flowchart showing a motor drive control routine executed byan electronic control unit 40 in the motor control apparatus 20 of theembodiment;

FIG. 3 is a map showing variations in motor toque demand Tm* againstvehicle speed V and accelerator opening Acc;

FIG. 4 is a flowchart showing a skid state determination routineexecuted by the electronic control unit 40 in the motor controlapparatus 20 of the embodiment;

FIG. 5 shows a variation in angular acceleration α against time;

FIG. 6 is a flowchart showing a skid occurring state control routineexecuted by the electronic control unit 40 in the motor controlapparatus 20 of the embodiment;

FIG. 7 is a map showing a variation in maximum torque Tmax againstangular acceleration α;

FIG. 8 is a flowchart showing a skid convergence state control routineexecuted by the electronic control unit 40 in the motor controlapparatus 20 of the embodiment;

FIG. 9 is a flowchart showing a torque restoration limit δ settingroutine executed by the electronic control unit 40 in the motor controlapparatus 20 of the embodiment;

FIG. 10 is a flowchart showing a torque restriction rate δlock settingroutine executed by the electronic control unit 40 in the motor controlapparatus 20 of the embodiment;

FIG. 11 shows a variation in angular acceleration α against time.

FIG. 12 is a map showing a variation in torque restriction rate δlockagainst the absolute negative peak value |αpeak2| of the angularacceleration α;

FIG. 13 schematically illustrates the configuration of a hybrid vehicle110;

FIG. 14 schematically illustrates the configuration of a hybrid vehicle210; and,

FIG. 15 schematically illustrates the configuration of a hybrid vehicle310.

BEST MODES OF CARRYING OUT THE INVENTION

Some modes of carrying out the invention are described below aspreferred embodiments. FIG. 1 schematically illustrates theconfiguration of an electric vehicle 10 equipped with a motor controlapparatus 20 in one embodiment of the invention. As illustrated, themotor control apparatus 20 of the embodiment is constructed to drive andcontrol a motor 12, which uses electric power supplied from a battery 16via an inverter circuit 14 and outputs power to a drive shaft linked todrive wheels 18 a, 18 b of the electric vehicle 10. The motor controlapparatus 20 includes a rotation angle sensor 22 that measures arotation angle θ of a rotating shaft of the motor 12, a vehicle speedsensor 24 that measures a driving speed of the vehicle 10, wheel speedsensors 26 a, 26 b, 28 a, and 28 b that respectively measure wheelspeeds of the drive wheels (front wheels) 18 a and 18 b and drivenwheels (rear wheels) 19 a and 19 b driven by the drive wheels 18 a and18 b, diversity of sensors that detect the driver's various operations(for example, a gearshift position sensor 32 that detects the driver'setting position of a gearshift lever 31, an accelerator pedal positionsensor 34 that detects the driver's step-on amount of an acceleratorpedal 33 (an accelerator opening), and a brake pedal position sensor 36that detects the driver's step-on amount of a brake pedal 35 (a brakeopening)), and an electronic control unit 40 that controls therespective constituents of the apparatus.

The motor 12 is, for example, a known synchronous motor generator thatfunctions both as a motor and a generator. The inverter circuit 14includes multiple switching elements that convert a supply of electricpower from the battery 16 into another form of electric power suitablefor actuation of the motor 12. The structures of the motor 12 and theinverter circuit 14 are well known in the art and are not the key partof this invention, thus not being described here in detail.

The electronic control unit 40 is constructed as a microprocessorincluding a CPU 42, a ROM 44 that stores processing programs, a RAM 46that temporarily stores data, and input and output ports (not shown).The electronic control unit 40 receives, via the input port, therotation angle θ of the rotating shaft of the motor 12 measured by therotation angle sensor 22, the vehicle speed V of the vehicle 10 measuredby the vehicle speed sensor 24, the wheel speeds Vf1 and Vf2 of thedrive wheels 18 a and 18 b and the wheel speeds Vr1 and Vr2 of thedriven wheels 19 a and 19 b measured by the wheel speed sensors 26 a, 26b, 28 a, and 28 b, the gearshift position detected by the gearshiftposition sensor 32, the accelerator opening Acc detected by theaccelerator pedal position sensor 34, and the brake opening detected bythe brake pedal position sensor 36. The electronic control unit 40outputs control signals, for example, switching control signals to theswitching elements of the inverter circuit 14 to drive and control themotor 12, via the output port.

The description regards the operations of the motor control apparatus 20constructed as discussed above, especially a series of operations ofdriving and controlling the motor 12 in the event of occurrence of askid due to wheelspin of the drive wheels 18 a and 18 b of the vehicle10. FIG. 2 is a flowchart showing a motor drive control routine executedby the electronic control unit 40 in the motor control apparatus 20 ofthe embodiment. This control routine is repeatedly executed at presettime intervals (for example, at every 8 msec).

When the motor drive control routine starts, the CPU 42 of theelectronic control unit 40 first inputs the accelerator opening Acc fromthe accelerator pedal position sensor 34, the vehicle speed V from thevehicle speed sensor 24, wheel speeds Vf and Vr from the wheel speedsensors 26 a, 26 b, 28 a, and 28 b, and a motor rotation speed Nmcalculated from the rotation angle θ measured by the rotation anglesensor 22 (step S100). In this embodiment, the wheel speeds Vf and Vrrespectively represent an average of the wheel speeds Vf1 and Vf2measured by the wheel speed sensors 26 a and 26 b and an average of thewheel speeds Vr1 and Vr2 measured by the wheel speed sensors 28 a and 28b. The vehicle speed V is measured by the vehicle speed sensor 24 inthis embodiment, but may alternatively be calculated from the wheelspeeds Vf1, Vf2, Vr1, and Vr2 measured by the wheel speed sensors 26 a,26 b, 28 a, and 28 b.

The CPU 42 then sets a torque demand Tm* of the motor 12 according tothe input accelerator opening Acc and the input vehicle speed V (stepS102). A concrete procedure of setting the motor torque demand Tm* inthis embodiment stores in advance variations in motor torque demand Tm*against the accelerator opening Acc and the vehicle speed V as a map inthe ROM 44 and reads the motor torque demand Tm* corresponding to thegiven accelerator opening Acc and the given vehicle speed V from themap. One example of this map is shown in FIG. 3.

The CPU 42 subsequently calculates an angular acceleration α from themotor rotation speed Nm input at step S100 (step S104). The calculationof the angular acceleration α in this embodiment subtracts a previousrotation speed Nm input in a previous cycle of this routine from acurrent rotation speed Nm input in the current cycle of this routine(current rotation speed Nm−previous rotation speed Nm). The unit of theangular acceleration α is [rpm/8 msec] since the execution interval ofthis routine is 8 msec in this embodiment, where the rotation speed Nmis expressed by the number of rotations per minute [rpm]. Any othersuitable unit may be adopted for the angular acceleration α as long asthe angular acceleration α is expressible as a time variation ofrotation speed. In order to minimize a potential error, the angularacceleration α may be an average of angular accelerations calculated ina preset number of cycles of this routine (for example, 3).

The CPU 42 determines a skid state of the drive wheels 18 a and 18 bbased on the calculated angular acceleration α (step S106), and executesa required series of control according to the result of thedetermination (steps S110 to S114), before terminating this motor drivecontrol routine. The determination of no occurrence of a skid (when botha skid occurrence flag F1 and a skid convergence flag F2 described beloware set equal to 0) triggers grip-state control (step S110). Thedetermination of the occurrence of a skid (when the flag F1 is set equalto 1 and the flag F2 is set equal to 0) triggers skid occurring statecontrol (step S112) to restrict the torque level output to the driveshaft. The determination of convergence of a skid (when both the flagsF1 and F2 are set equal to 1) triggers skid convergence state control(step S114) to restore the restricted torque level output to the driveshaft.

The determination of the skid state follows a skid state determinationroutine shown in FIG. 4. When the skid state determination routinestarts, the CPU 42 of the electronic control unit 40 compares theangular acceleration α calculated at step S104 in the control routine ofFIG. 2 with a preset threshold value αslip, which suggests theoccurrence of a skid due to wheelspin (step S120). When the calculatedangular acceleration α exceeds the preset threshold value αslip, the CPU42 determines the occurrence of a skid on the wheels 18 a and 18 b andsets the value ‘1’ to a skid occurrence flag F1 representing theoccurrence of a skid (step S122), in order to restrict the torque leveloutput to the drive shaft. The CPU 42 then exits from this skid statedetermination routine. When the calculated angular acceleration α doesnot exceed the preset threshold value αslip, on the other hand, the CPU42 determines whether the skid occurrence flag F1 is equal to 1 (stepS124). When the skid occurrence flag F1 is equal to 1, the CPU 42subsequently determines whether the current angular acceleration α isnot less than 0 while the previous angular acceleration α in theprevious cycle of this routine is less than 0, that is, whether theangular acceleration α rises from a negative value and passes over azero cross point (step S126). In the case of an affirmative answer, theCPU 42 determines that the skid occurring on the drive wheels 18 a and18 b is converged and that now is the adequate restoration timing of therestricted torque level output to the drive shaft and sets the value ‘1’to a skid convergence flag F2 (step S128). The CPU 42 then exits fromthis skid state determination routine.

FIG. 5 shows a variation in angular acceleration α against time. Asshown in FIG. 5, in the course of restriction of the torque level outputto the drive shaft in response to the occurrence of a skid, the angularacceleration α first increases with elapse of time to give a positivepeak, then decreases to give a negative peak, and again increases. Theadequate restoration timing of the restricted torque level output to thedrive shaft is a zero cross point of the angular acceleration α afterthe negative peak. The zero cross timing enables the direction of thetorque applied on the drive shaft in the course of restoration from thetorque restriction to be completely identical with the direction of theangular acceleration α applied on the drive shaft, thus preventingpotential torsional vibrations of the drive shaft. In the case of anegative answer at step S126, on the other hand, the CPU 42 determinesthat the skid has not yet been converged or that now is not the adequaterestoration timing of the restricted torque level output to the driveshaft even under the condition of convergence of the skid and terminatesthis skid state determination routine. When the calculated angularacceleration α does not exceed the preset threshold value αslip and theskid occurrence flag F1 is not equal to 1, the CPU 42 sets both the skidoccurrence flag F1 and the skid convergence flag F2 equal to 0 (stepS130) and terminates this skid state determination routine. Therespective controls executed according to the values of the skidoccurrence flag F1 and the skid convergence flag F2 are described indetail below.

The grip state control is normal drive control of the motor 12 anddrives and controls the motor 12 to ensure output of a torquecorresponding to the preset torque demand Tm*.

The skid occurring state control drives and controls the motor 12 tolower the angular acceleration α, which was increased by the occurrenceof a skid, and follows a skid occurring state control routine of FIG. 6.The CPU 42 of the electronic control unit 40 first compares the angularacceleration α with a preset peak value αpeak (step S140). When theangular acceleration α exceeds the preset peak value αpeak, the currentvalue of the angular acceleration α is newly set to the peak value αpeak(step S142). The peak value αpeak represents a peak of the angularacceleration α increasing due to a skid and is initially set equal to 0.Until the angular acceleration α increases to reach its maximum, thepeak value αpeak is successively updated to the current value of theangular acceleration α. When the increasing angular acceleration αreaches its maximum, the maximum value of the increasing angularacceleration α is fixed to the peak value αpeak. After setting the peakvalue αpeak, the CPU 42 sets a maximum torque Tmax as an upper limit oftorque output from the motor 12 corresponding to the peak value αpeak(step S144). The procedure of this embodiment refers to a map shown inFIG. 7 to set the maximum torque Tmax. FIG. 7 shows a variation inmaximum torque Tmax against the angular acceleration α. As illustratedin this map, the maximum torque Tmax decreases with an increase inangular acceleration α. The greater peak value αpeak with an increase inangular acceleration α, that is, the heavier skid, sets the smallervalue to the maximum torque Tmax and limits the output torque of themotor 12 to the smaller maximum torque Tmax.

After setting the maximum torque Tmax, the motor torque demand Tm* iscompared with the maximum torque Tmax (step S146). When the motor torquedemand Tm* exceeds the maximum torque Tmax, the motor torque demand Tm*is limited to the maximum torque Tmax (step S148). The CPU 42 thendetermines whether a torque restriction width (a torque variation) givenas a difference between the current motor torque demand Tm* and aprevious motor torque demand Tm* set in the previous cycle of thisroutine (Tm*−Previous Tm*) is in a preset allowable range (step S150).When the torque variation is not in the preset allowable range, themotor torque demand Tm* is regulated to limit the torque variation inthe preset allowable range (step S152). Such regulation of the motortorque demand Tm* reduces a potential torque shock caused by significantrestriction of the torque level output to the drive shaft in response tothe occurrence of a skid. The CPU 42 then sets the motor torque demandTm* to a target torque and drives and controls the motor 12 to output atorque corresponding to the target torque Tm* (step S154), beforeexiting from this skid occurring state control routine. The torqueoutput from the motor 12 in the occurrence of a skid is limited to alower level (that is, the maximum torque Tmax corresponding to the peakvalue αpeak of the angular acceleration in the map of FIG. 7) forimmediate reduction of the skid. This limitation effectively reduces theskid.

The skid convergence state control drives and controls the motor 12 torestore the limited torque level, when the torque restriction by theskid occurring state control lowers the angular acceleration α andconverges the skid. The skid convergence state control follows a skidconvergence state control routine of FIG. 8. The CPU 42 of theelectronic control unit 40 first inputs a torque restoration limit δ(expressed in the same unit [rpm/8 msec] as the angular acceleration)(step S160).

The torque restoration limit δ is a parameter used to set a degree ofrestoration from the torque restriction by increasing the maximum torqueTmax, which has been set in the skid occurring state control describedabove. The initial value of the torque restoration limit δ is set equalto 0. The torque restoration limit δ is set according to a torquerestoration limit δ setting routine shown in FIG. 9 as discussed below.The torque restoration limit δ setting routine of FIG. 9 is executedwhen the skid occurrence flag F1 is set from 0 to 1 (that is, when thecalculated angular acceleration α exceeds the preset threshold valueαslip) at step S122 in the skid state determination routine of FIG. 4.This routine inputs the motor rotation speed Nm calculated from therotation angle θ measured by the rotation angle sensor 22, calculatesthe angular acceleration α of the motor 12 from the input motor rotationspeed Nm, and integrates the angular acceleration α to give a timeintegration αint thereof over an integration interval since the angularacceleration α exceeded the preset threshold value αslip. These input,calculation, and integration steps are repeated until the angularacceleration α decreases below the preset threshold value αslip (stepsS190 to S196). In this embodiment, the time integration αint of theangular acceleration α is given by Equation (1) below, where Δt denotesa time interval of the repeated execution of steps S190 to S196 and isset equal to 8 msec in this embodiment:αint←αint+(α−αslip)·Δt   (1)

When the angular acceleration α decreases below the preset thresholdvalue αslip, the time integration αint of the angular acceleration aobtained by the processing of steps S190 to S196 is multiplied by apredetermined coefficient k to set the torque restoration limit δ (stepS198). The torque restoration limit δ setting routine is hereterminated. The concrete process of setting the torque restoration limitδ writes the value of the torque restoration limit δ into a specificarea of the RAM 46.

Referring back to the routine of FIG. 8, after input of the torquerestoration limit δ at step S160, the CPU 42 inputs a cancellationrequest of canceling the torque restoration limit δ if any (step S162)and determines whether the cancellation request has been entered (stepS164). In this embodiment, a torque restriction cancellation routine(not shown) is executed after elapse of a predetermined standby timesince the start of execution of the skid convergence state controlroutine. The torque restriction cancellation routine sets a cancellationrate Δδ to increment from zero by a fixed value on every elapse of apreset time period. Cancellation of the torque restoration limit δ doesnot start until elapse of the predetermined standby time since the startof execution of the routine of FIG. 7. In the event of detection of acancellation request, the CPU 42 subtracts the cancellation rate Δδ fromthe torque restoration limit δ input at step S160 to cancel the torquerestoration limit δ (step S166). In the event of no detection of acancellation request, on the other hand, the torque restoration limit δinput at step S160 is not cancelled. The CPU 42 then refers to the mapof FIG. 7 and sets the maximum torque Tmax as an upper limit of torqueoutput from the motor 12 corresponding to the torque restoration limit δ(step S168).

The CPU 42 determines whether a torque restriction rate δlock [rpm/8msec] has been set (step S170). Under the condition of setting thetorque restriction rate δlock, the maximum torque Tmax is setcorresponding to the torque restriction rate δlock by referring to themap of FIG. 7, regardless of the setting at step S168 (step S172). Thetorque restriction rate δlock is a parameter set to control thevibration of the drive shaft due to an abrupt negative change of theangular acceleration α, which arises when the vehicle 10 moves to a highμ road after a skid on a low μ road. The torque restriction rate δlockis set according to a torque restriction rate δlock setting routine ofFIG. 10. The torque restriction rate δlock setting routine is executedwhen the skid occurrence flag F1 is set from 0 to 1. This routine inputsthe motor rotation speed Nm calculated from the rotation angle θmeasured by the rotation angle sensor 22 and calculates the angularacceleration α from the input motor rotation speed Nm. When thecalculated angular acceleration α reaches a negative peak, that is, whena time difference of the angular acceleration α changes from negative topositive, the angular acceleration α at the moment is set to a negativepeak value αpeak2 (steps S200 to S206). The absolute negative peak value|αpeak2| is then compared with a predetermined threshold value αref(step S208).

FIG. 11 shows a variation in angular acceleration α against time underthe condition of a change of the road surface condition. Under thecondition of no change of the road surface condition, the negative peakappearing in the course of convergence of the wheelspin of the drivewheels 18 a and 18 b is in a preset range as shown in FIG. 5. Under thecondition of a change of the road surface condition from the low μ roadto the high μ road in the presence of a skid, however, the angularacceleration α has an abrupt negative change to make the negative peakexceed the preset range. A change of the road surface condition isaccordingly assumed when the absolute negative peak value |αpeak2| ofthe angular acceleration α exceeds the predetermined threshold valueαref.

When the absolute negative peak value |αpeak2| exceeds the predeterminedthreshold value αref, the torque restriction rate δlock is setcorresponding to the absolute negative peak value |αpeak2| (step S200).After elapse of a preset time period (step S202), the routine cancelsthe torque restriction rate δlock (step S204) and is terminated. Aconcrete procedure of setting the torque restriction rate δlock in thisembodiment stores in advance a variation in torque restriction rateδlock against the absolute negative peak value |αpeak2| as a map in theROM 44 and reads the torque restriction rate δlock corresponding to agiven absolute negative peak value |αpeak2|. One example of this map isshown in FIG. 12. As shown in the map of FIG. 12, the torque restrictionrate δlock increases with an increase in absolute negative peak value|αpeak2|. The smaller maximum torque Tmax is set against the greatertorque restriction rate δlock (see FIG. 7), so that a smaller value isset to the maximum torque Tmax corresponding to the greater absolutenegative peak value |αpeak2|. The torque restriction rate δlock is keptunchanged until elapse of the preset time period. The routine of FIG. 8is repeatedly executed to effectuate the torque restriction with settingof the torque restriction rate δlock in the preset time period. Therepeated execution in the preset time period effectively controls apotential vibration of the angular acceleration α (vibration of thedriving system), which may arise in response to a change of the roadsurface condition. The preset time period may be an expected vibrationconvergence time measured experimentally. The solid line curve in FIG.11 shows a time variation of the angular acceleration α under thecondition of torque restriction with setting of the torque restrictionrate δlock. The broken line curve shows a time variation of the angularacceleration α under the condition of no torque restriction with thetorque restriction rate δlock. The procedure of this embodimentcompletely cancels out the setting of the torque restriction rate δlockat a time after elapse of the preset time period. One modified proceduremay cancel the setting of the torque restriction rate δlock in astepwise manner.

Referring back to the routine of FIG. 8, after setting the maximumtorque Tmax, the motor torque demand Tm* is compared with the presetmaximum torque Tmax (step S174). When the motor torque demand Tm*exceeds the maximum torque Tmax, the motor torque demand Tm* is limitedto the maximum torque Tmax (step S176). The CPU 42 then sets the motortorque demand Tm* to a target torque and drives and controls the motor12 to output a torque corresponding to the target torque Tm* (stepS178). The CPU 42 determines whether the torque restoration limit δ1 isnot greater than zero, that is, whether the torque restoration limit δ1has been cancelled out completely (step S180). In the event of perfectcancellation of the torque restoration limit δ, both the slip occurrenceflag F1 and the slip convergence flag F2 are reset to 0 (step S182).

As described above, the motor control apparatus 20 of the embodimentrestricts the torque level output to the drive shaft in response todetection of a skid caused by the wheelspin of the drive wheels 18 a and18 b, and restores the restricted torque level at the zero cross timingof the angular acceleration α of the rotating shaft of the motor 12after the negative peak value αpeak 2. The torque control makes thedirection of the torque completely identical with the direction of theangular acceleration. This arrangement desirably prevents potentialtorsional vibrations of the drive shaft and the vibration of the angularacceleration α. When the absolute negative peak value |αpeak2| of theangular acceleration α reflecting a change of the road surface conditionexceeds the predetermined threshold value αref, the output torque levelis restricted according to the negative peak value αpeak2. Thisarrangement desirably prevents potential vibrations of the drive shaftdue to a change of the road surface condition.

The motor control apparatus 20 of the embodiment sets the motor torquedemand Tm* to limit the torque variation in the specified allowablerange, in the case where the torque variation is out of the specifiedallowable range in the course of restriction of the torque level outputto the drive shaft in response to the occurrence of a skid due to thewheelspin of the drive wheels 18 a and 18 b. This arrangementeffectively prevents an excess torque shock (vibration of the driveshaft), which may be caused by torque restriction in response to theoccurrence of a skid.

The motor control apparatus 20 of the embodiment restores the restrictedtorque level at the zero cross timing of the angular acceleration α ofthe rotating shaft of the motor 12. The restricted torque level may berestored at any timing when the direction of the torque is identicalwith the direction of the angular acceleration, that is, at any timingin the course of an increase in angular acceleration α after thenegative peak value αpeak2.

The motor control apparatus 20 of the embodiment specifies the allowablerange of torque variation and sets the motor torque demand Tm* to limitthe torque variation in the specified allowable range in the course ofrestriction of the torque level output from the motor 12 in response todetection of a skid. One modified procedure may set the motor torquedemand Tm* without specifying the allowable range.

The motor control apparatus 20 of the embodiment reads the torquerestriction rate δlock corresponding to the negative peak value αpeak2of the angular acceleration α from the map of FIG. 12, and sets themaximum torque Tmax corresponding to the torque restriction rate δlockin the map of FIG. 7 to attain torque restriction. One modifiedprocedure may directly set the maximum torque Tmax corresponding to thenegative peak value αpeak2 of the angular acceleration α to attaintorque restriction.

The motor control apparatus 20 of the embodiment may adopt a levelingtechnique in the process of restricting the torque level output to thedrive shaft and in the process of restoring the restricted torque leveloutput to the drive shaft. This enhances the effect of controlling thetransmission of vibrations to the drive shaft.

The embodiment described above regards control of the motor 12, which ismounted on the vehicle 10 and is mechanically connected with the driveshaft linked to the drive wheels 18 a and 18 b to directly output powerto the drive shaft. The technique of the invention is applicable to avehicle of any other structure with a motor that is capable of directlyoutputting power to a drive shaft. For example, one possible applicationof the invention is a series hybrid vehicle including an engine, agenerator that is linked to an output shaft of the engine, a batterythat is charged with electric power generated by the generator, and amotor that is mechanically connected with a drive shaft linked to drivewheels and is driven with a supply of electric power from the battery.Another possible application of the invention is a mechanicaldistribution-type hybrid vehicle 110 including an engine 111, aplanetary gear 117 that is connected with the engine 111, a motor 113that is connected with the planetary gear 117 and is capable ofgenerating electric power, and a motor 112 that is also connected withthe planetary gear 117 and is mechanically connected with a drive shaftlinked to drive wheels to directly output power to the drive shaft, asshown in FIG. 13. Still another possible application of the invention isan electrical distribution-type hybrid vehicle 210 including a motor 213that has an inner rotor 213 a connected with an output shaft of anengine 211 and an outer rotor 213 b connected with a drive shaft linkedto drive wheels 218 a and 218 b and relatively rotates throughelectromagnetic interactions between the inner rotor 213 a and the outerrotor 213 b and a motor 212 that is mechanically connected with thedrive shaft to directly output power to the drive shaft, as shown inFIG. 14. Another possible application of the invention is a hybridvehicle 310 including an engine 311 that is connected with a drive shaftlinked to drive wheels 318 a and 318 b via a transmission 314 (forexample, a continuous variable transmission or an automatictransmission) and a motor 312 that is placed after the engine 311 and isconnected with the drive shaft via the transmission 314 (or a motor thatis directly connected with the drive shaft), as shown in FIG. 15. In theevent of the occurrence of a skid on drive wheels, the torque controlmainly controls the motor mechanically connected with the drive shaft,because of its high torque output response. The control of this motormay be combined with control of the other motor or with control of theengine.

The embodiment and its modified examples discussed above are to beconsidered in all aspects as illustrative and not restrictive. There maybe many other modifications, changes, and alterations without departingfrom the scope or spirit of the main characteristics of the presentinvention.

INDUSTRIAL APPLICABILITY

The technique of the invention is effectively applied to automobile andtrain-related industries.

1. A motor control apparatus that controls a motor, which is mounted on a vehicle and outputs power to a drive shaft linked to drive wheels, said motor control apparatus comprising: an angular acceleration measurement module that measures an angular acceleration of either the drive shaft or a rotating shaft of said motor; a skid detection module that detects occurrence of a skid due to wheelspin of the drive wheels, in response to an increase in measured angular acceleration over a preset value; a first torque restriction control module that, in response to detection of the occurrence of a skid by said skid detection module, sets a certain torque restriction rate to restrict an output torque level for reduction of the skid and controls said motor with the restricted output torque level; and a torque restoration control module that restores the output torque level restricted by said first torque restriction control module and controls said motor with the restored output torque level at a predetermined timing when the angular acceleration measured by said angular acceleration measurement module has an increase in the course of convergence of the skid.
 2. A motor control apparatus in accordance with claim 1, wherein the predetermined timing represents a change timing of the measured angular acceleration from negative to positive.
 3. A motor control apparatus in accordance with claim 1, wherein said torque restoration control module controls said motor with a lower torque restriction rate than the certain torqu restriction rate set by said first torque restriction control module for a preset time period, so as to restore the restricted output torque level.
 4. A motor control apparatus in accordance with claim 1, said motor control apparatus further comprising: a second torque restriction control module that controls said motor with setting of a specified torque restriction, when an absolute value of a first negative peak of the measured angular acceleration detected after the increase over the preset value is greater than a predetermined threshold value.
 5. A motor control apparatus in accordance with claim 4, wherein said second torque restriction control module controls said motor with a torque restriction rate set corresponding to the absolute value of the first negative peak as the specified torque restriction.
 6. A motor control apparatus in accordance with claim 4, wherein said second torque restriction control module controls said motor with the setting of the specified torque restriction for a predetermined time period.
 7. A motor control apparatus in accordance with claim 1, wherein said first torque restriction control module controls said motor to have a torque variation in a preset allowable range.
 8. A motor control apparatus that controls a motor, which is mounted on a vehicle and outputs power to a drive shaft linked to drive wheels, said motor control apparatus comprising: a skid detection module that detects occurrence of a skid due to wheelspin of the drive wheels; a torque restriction rate setting module that, in response to detection of the occurrence of a skid by said skid detection module, sets a torque restriction rate of torque output to the drive shaft corresponding to a degree of the detected skid; a torque restriction rate correction module that, when control of said motor with the set torque restriction rate makes a torque variation out of a preset allowable range, corrects the torque restriction rate to limit the torque variation in the preset allowable range; and a torque restriction control module that controls said motor, based on a power demand to the drive shaft and the set or corrected torque restriction rate.
 9. A motor control apparatus in accordance with claim 8, said motor control apparatus further comprising: an angular acceleration measurement module that measures an angular acceleration of either the drive shaft or a rotating shaft of said motor, wherein said skid detection module detects the occurrence of a skid when the measured angular acceleration exceeds a predetermined threshold value, and in response to detection of the occurrence of a skid by said skid detection module, said torque restriction rate setting module sets the torque restriction rate of torque output to the drive shaft corresponding to the angular acceleration measured by said angular acceleration measurement module.
 10. A motor control apparatus in accordance with claim 9, wherein said torque restriction rate setting module increases the torque restriction rate with an increase in angular acceleration.
 11. A vehicle, including: a motor control apparatus that controls a motor, which is mounted on the vehicle and outputs power to a drive shaft linked to drive wheels, said motor control apparatus comprising: an angular acceleration measurement module that measures an angular acceleration of either the drive shaft or a rotating shaft of said motor; a skid detection module that detects occurrence of a skid due to wheelspin of the drive wheels, in response to an increase in measured angular acceleration over a preset value; a first torque restriction control module that, in response to detection of the occurrence of a skid by said skid detection module, sets a certain torque restriction rate to restrict an output torque level for reduction of the skid and controls said motor with the restricted output torque level; and a torque restoration control module that restores the output torque level restricted by said first torque restriction control module and controls said motor with the restored output torque level at a predetermined timing when the angular acceleration measured by said angular acceleration measurement module has an increase in the course of convergence of the skid.
 12. A motor control method that controls a motor, which is mounted on a vehicle and outputs power to a drive shaft linked to drive wheels, said motor control method comprising the steps of: (a) measuring an angular acceleration of either the drive shaft or a rotating shaft of said motor; (b) detecting occurrence of a skid due to wheelspin of the drive wheels, in response to an increase in measured angular acceleration over a preset value; (c) in response to detection of the occurrence of a skid, selling a certain torque restriction rate to restrict an output torque level for reduction of the skid and controlling said motor with the restricted output torque level; and (d) restoring the output torque level restricted in said step (c) and controlling said motor with the restored output torque level at a predetermined timing when the angular acceleration measured in said step (a) has an increase in the course of convergence of the skid by the restriction of the output torque level.
 13. A motor control method in accordance with claim 12, wherein the predetermined timing represents a change timing of the measured angular acceleration from negative to positive.
 14. A motor control method in accordance with claim 12, wherein said step (d) controls said motor with a lower torque restriction rate than the certain torque restriction rate set by said step (C) for a preset time period, so as to restore the restricted output torque level.
 15. A motor control method in accordance with claim 12, said motor control method further comprising the step of: (e) controlling said motor with setting of a specified torque restriction, when an absolute value of a first negative peak of the measured angular acceleration detected after the increase over the preset value is greater than a predetermined threshold value.
 16. A motor control method in accordance with claim 15, wherein said step (e) controls said motor with a torque restriction rate set corresponding to the absolute value of the first negative peak as the specified torque restriction.
 17. A motor control method in accordance with claim 15, wherein said step (e) controls said motor with the setting of the specified torque restriction for a predetermined time period.
 18. A motor control method that controls a motor, which is mounted on a vehicle and outputs power to a drive shaft linked to drive wheels, said motor control method comprising the steps of: (a) detecting occurrence of a skid due to wheelspin of the drive wheels; (b) in response to detection of the occurrence of a skid by said step (a), setting a torque restriction rate of torque output to the drive shaft corresponding to a degree of the detected skid; (c) when control of said motor with the set torque restriction rate makes a torque variation out of a preset allowable range, correcting the torque restriction rate to limit the torque variation in the preset allowable range; and (d) controlling said motor, based on a power demand to the drive shaft and the set or corrected torque restriction rate.
 19. A motor control method in accordance with claim 18, said motor control method further comprising the step of: (e) measuring an angular acceleration of either the drive shaft or a rotating shaft of said motor, prior to said step (a) wherein said step (a) detects the occurrence of a skid when the angular acceleration measured by said step (e) exceeds a predetermined threshold value, and in response to detection of the occurrence of a skid by said step (a), said step (b) sets the torque restriction rate of torque output to the drive shaft corresponding to the angular acceleration measured by said step (e).
 20. A motor control method in accordance with claim 19, wherein said step (b) increases the torque restriction rate with an increase in angular acceleration. 